As a technique for measuring a flow rate of gas, in general, there is known a heating resistor type air flow rate measuring apparatus for measuring a flow rate of air. This measuring apparatus utilizes the relation that an amount of heat absorbed from the heating resistor increases monotonously in accordance with the increase of an flow rate of air. Since this measuring apparatus can directly measure a mass air flow rate, this measuring apparatus is used widely as a flow meter for measuring an air flow rate for the internal combustion engine of an automobile.
An air cleaner is provided at the upstream portion of the suction pipe of the internal combustion engine, whereby air from which dust within the atmosphere is removed is supplied within the engine.
However, since the dust collecting ability of the air cleaner is not complete, fine dust component etc. passes the air cleaner and is sucked into the engine via the suction pipe.
Since the heating resistor type air flow rate measuring apparatus is provided in a manner that the heating resistor serving as a flow rate measuring portion is exposed within the suction pipe, the heating resistor deteriorates with age due to the adhesion of dust etc. thereto as described above.
Thus, there is known a technique as described in a patent document 1(JP-A-63-41644) that a heating resistor is heated at about 100° C. after stopping an engine thereby to burn dust component etc. adhered to the heating resistor.